let me count the ways…
infinity plus 1) you think you are smart but you are not,
infinity plus 2) you do not give the people the power they need to help out when you are not smart — see number 1.
I simply wanted to upgrade my 1TB of software raid 1 to 1.5 TB of software raid 1, besides the time for copying and syncing it should be a slam dunk, but thanks to grub2 it was a super utter cluster f*ck.
I started by transitioning to a non mirrored 1.5 Tb disk with boot, swap and root, then after I was able to boot that, I built a set of degraded raid1’s on the other disk and then tried to bring the the first 1.5.
however my partition on the first half of the degraded raid was slightly larger than partition on the second half, I tried to resize it but then it wouldn’t boot… so I got to do the whole 1TB copy with billions of hard links over again… These are the steps to resize a raided partition if you are not using it for root http://www.howtoforge.com/how-to-resize-raid-partitions-shrink-and-grow-software-raid
Finally on the system 10 days later, still need to add the other half of the degraded disk, but this time they are the same size.
For grub2 help this page was helpful, (mostly pages 2 and 3): http://www.howtoforge.com/how-to-set-up-software-raid1-on-a-running-system-incl-grub2-configuration-ubuntu-10.04
I also manually updated the device map /boot/grub/device.map which may have helped things, dunno…
There was a post I read along the way but can’t find the URL that talked about using chroot, after mounting some things like dev and proc into the future chroot, that sounded promising, but I didn’t have to do that.
I also tried a shit ton of different ways to tell grub to boot my degraded mirror, ran grub-install, update-grub, and update-initramfs many, many, many times, what ultimately seemed to work was to run update-grub and grub-install again after I hacked my way to getting grub to boot up with root on /dev/md2. After the raid is done re-syncing I’ll try to pull the half that I built first and try to boot from the new half.